Radiation to Actinometric Receivers in Its Dependence on Aperture Conditions

After an introduction on basic conceptions, concerning the influence of aperture conditions on the readings of actinometers, a short review is given on recent results as regards the arcumsolar sky radiation. The combined effect of aperture and sky radiation on pyrheliometric readings, in the case of point receivers, is discussed. Conclusions are drawn as regards the influence of aperture conditions on (a) solar constant determinations and (b) on the difference between readings with aid of different pyrheliometers. The principles which ought to be applied in the construction of pyrheliometers for different kind of use, are briefiy discussed.